Development of mass-production technique of the ATLAS thin gap chamber in Japan

The thin gap chambers (TGCs) are used for the muon trigger system in the end-cap regions of the ATLAS detector. As the anode-cathode distance is small, 1.4 mm, chamber flatness is essential to achieve a uniform gas gain over the chamber. The TGC mass production phase at High Energy Accelerator Research Organization (KEK) started in January 2001. In order to perform a stable production with high quality we developed a chamber closing system. When we glue two half- chambers together, we sandwich them with a granite table and an aluminum honeycomb panel that keep the chamber flat from both sides. By using silk screens, we also control the quantity of epoxy adhesive that affects the chamber thickness. Owing to these developments, we can achieve the flatness of less than 100 mu m. Uniformity of detection efficiency of the TGC is measured with a cosmic-ray test bench at Kobe University. We have tested 300 TGCs so far. Position dependence of the efficiency is measured with a granularity of 5 mm- by-5 mm. The average efficiency over the tested chambers is achieved to be 99 % excluding the wire supports and spacers. (9 refs).